Combustion-powered linear motors are used within combustion-powered tools, such as, for example, tools which are utilized to drive fasteners or other projectiles, wherein the combustion-powered linear motors are intermittently or cyclically operated or actuated, as opposed to being continuously operated as in the case of conventional internal combustion engines, in order to drive or discharge the fasteners or projectiles out from the tools at predetermined times. The combustion-powered linear motors comprise power pistons which undergo power strokes whereby the power pistons cause the fasteners or projectiles to be driven or discharged out from the tools, and subsequently, the combustion chambers of the combustion-powered linear motors need to be scavenged or purged so as to effectively rid the same of residual combustion products or exhaust gases which have been generated during the previous combustion cycle. Failure to properly scavenge or purge the combustion chambers of such residual combustion products or exhaust gases will adversely affect the proper or required stoichiometric ratio of the new or fresh air-fuel mixtures to be charged into the combustion chambers. Accordingly, improper or insufficient power levels will be developed or achieved within the combustion chambers whereby the power pistons will be unable to properly drive or discharge the fasteners or other projectiles out from the combustion-powered tools. In addition, it is also imperative that the aforenoted scavenging or purging of the residual combustion products or exhaust gases be achieved as quickly as possible so as to not only facilitate the rapid operative recycling of the combustion-powered tools, that is, to enable or ready the combustion-powered tools for subsequent firing cycles, but in addition, to effectively prevent the overheating of the combustion-powered tools.
An example of an intermittently operated combustion powered linear motor, and a scavenging system therefor, is disclosed within U.S. Pat. No. 6,932,031 which issued to Adams on Aug. 23, 2003. As can be appreciated from FIG. 1, which substantially corresponds to FIG. 1 of the aforenoted Adams patent, the aforenoted patented system comprises a combustion chamber 2 within which there is disposed a spark plug 6. A power piston 8 is disposed within a piston cylinder, and a return spring 30 is also disposed within the piston cylinder so as to be interposed between the undersurface portion of the power piston 8 and the lower or bottom wall portion of the piston cylinder whereby the return spring 30 serves to return the power piston 8 to its original start position upon completion of its power stroke as a result of the ignition of the air/fuel mixture within the combustion chamber 2. The region of the piston cylinder, which is disposed beneath the power piston 8, is fluidically connected to the lower end portion of a plenum chamber 4 through means of a first check valve 12, and the upper end portion of the plenum chamber 4 is fluidically connected to the combustion chamber 2 through means of a second check valve 24. Still further, a third check valve 17 is provided within the lower end portion of the piston cylinder so as to permit fresh or ambient air to enter the lower end portion of the piston cylinder, and the combustion chamber 2 is provided with an exhaust valve 16 to which a piston-type actuator 14 is operatively connected. In addition, a fluid signal line 13 fluidically interconnects plenum chamber 4 with the piston cylinder within which the piston-type actuator 14 is disposed.
It can therefore be readily appreciated that during the downward movement or power stroke of the power piston 8, fresh or ambient air, which has been previously been admitted into the lower end portion of the piston cylinder through means of the third check valve 17, will be compressed and forced into the plenum chamber 4. In addition, the compressed air will also be conducted through the fluid signal line 13 so as to enter the piston cylinder within which the piston-type actuator 14 is disposed, however, during the early part of the combustion cycle, the pressure developed within the combustion chamber 2 is greater than the pressure of the compressed air within plenum chamber 4 such that the second check valve 24 and exhaust valve 16 remain closed. However, when the power piston 8 nears, approaches, and is substantially at, the end of its downward movement or power stroke, at which time the pressure prevailing within the combustion chamber 2 will have decreased, both the exhaust valve 16 and the second check valve 24 will be opened so as to achieve the scavenging or purging of the combustion chamber 2. While the aforenoted system is operationally satisfactory, it is believed that a structurally simpler, quicker, and more efficient combustion scavenging or purging process would be more beneficial. More particularly, it is seen that as the power piston 8 of Adams approaches or nears the end of its downward movement or power stroke, and subsequently begins to move upwardly during its return stroke, the scavenging or purging of the combustion chamber 2, by means of the scavenging or purging air disposed within the plenum chamber 4, is, in effect, solely dependent upon the elevated pressure level present within the plenum chamber 4, that is, the pressure level present within the plenum chamber 4 is effectively the sole force causing the scavenging or purging air to flow from the plenum chamber 4 into the combustion chamber 2.
A need therefore exists in the art for a new and improved combustion-powered linear air motor/compressor, for use within combustion-powered tools, wherein the scavenging or purging air will be rammed or forced into, through, and out of the combustion chamber during the return stroke of the power piston assembly so as to rapidly and efficiently scavenge or purge the residual combustion products or exhaust gases from the combustion chamber of the combustion-powered tool.